Field of the Disclosure
The present disclosure generally relates to a genset for a top drive unit.
Description of the Related Art
A wellbore is formed to access hydrocarbon-bearing formations (e.g., crude oil and/or natural gas) or for geothermal power generation by the use of drilling. Drilling is accomplished by utilizing a drill bit that is mounted on the end of a drill string. To drill within the wellbore to a predetermined depth, the drill string is often rotated by a top drive on a surface rig. After drilling to a predetermined depth, the drill string and drill bit are removed and a section of casing is lowered into the wellbore. An annulus is thus formed between the string of casing and the formation. The casing string is hung from the wellhead. A cementing operation is then conducted in order to fill the annulus with cement. The casing string is cemented into the wellbore by circulating cement into the annulus defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
Top drives are equipped with a motor for rotating the drill string. The quill of the top drive is typically threaded for connection to an upper end of the drill pipe in order to transmit torque to the drill string. The top drive may also have various accessories to facilitate drilling. For adapting to the larger casing string, the drilling accessories are removed from the top drive and a casing running tool is added to the top drive. The casing running tool has a threaded adapter for connection to the quill and grippers for engaging an upper end of the casing string. It would be useful to have sensors on the casing running tool to monitor operation thereof. Transmitting electricity from a stationary power source to the rotating casing running tool is problematic. Electrical slip rings are not practical because the top drive operates in a harsh environment where components are exposed to shock and vibration. Moreover, because slip rings can spark during operation, they require complex measures, such as flameproof housings or purging with air for use in the explosive atmospheres that sometime occur during casing running operations. Slip rings also utilize brushes requiring frequent replacement. It would be beneficial to provide a local source of electrical power for the various accessories that facilitate drilling.